﻿Principle 
  of 
  Relativity 
  and 
  Non-Newtonian 
  Mechanics, 
  511 
  

  

  reason, 
  but 
  recent 
  experimental 
  evidence, 
  to 
  which 
  we 
  shall 
  

   revert, 
  seems 
  to 
  prove 
  it 
  untenable. 
  

  

  This 
  possibility 
  being 
  excluded, 
  the 
  only 
  satisfactory 
  

   explanation 
  o£ 
  the 
  Michelson-Morley 
  experiment 
  which 
  has 
  

   been 
  offered 
  is 
  due 
  to 
  Lorentz 
  *, 
  who 
  assumed 
  that 
  all 
  bodies 
  

   in 
  motion 
  are 
  shortened 
  in 
  the 
  line 
  of 
  their 
  motion 
  by 
  an 
  

   amount 
  which 
  is 
  a 
  simple 
  function 
  of 
  the 
  velocity. 
  This 
  

   shorteniuor 
  ^Yould 
  produce 
  a 
  compensation 
  just 
  sufficient 
  to 
  

   offset 
  the 
  predicted 
  positive 
  effect 
  in 
  the 
  Michelson-Morley 
  

   experiment, 
  and 
  would 
  also 
  account 
  for 
  the 
  result 
  obtained 
  

   by 
  Trouton 
  and 
  Noble. 
  It 
  would 
  not, 
  however, 
  prevent 
  the 
  

   determination 
  of 
  absolute 
  motion 
  by 
  other 
  analogous 
  experi- 
  

   ments 
  which 
  have 
  not 
  yet 
  been 
  tried. 
  

  

  Einstein 
  f 
  has 
  gone 
  one 
  step 
  farther. 
  Because 
  of 
  the 
  

   experiments 
  that 
  we 
  have 
  cited, 
  and 
  because 
  of 
  the 
  failure 
  of 
  

   every 
  other 
  attempt 
  that 
  has 
  ever 
  been 
  made 
  to 
  determine 
  

   absolute 
  velocity 
  through 
  space, 
  he 
  concludes 
  that 
  further 
  

   similar 
  attempts 
  will 
  also 
  fail. 
  In 
  fact 
  he 
  states 
  as 
  a 
  law 
  of 
  

   nature 
  that 
  absolute 
  uniform 
  translatory 
  motion 
  can 
  be 
  neither 
  

   measured 
  nor 
  detected. 
  

  

  The 
  second 
  fundamental 
  generalization 
  made 
  by 
  Einstein 
  

   he 
  calls 
  " 
  the 
  law 
  of 
  the 
  constancy 
  of 
  light 
  velocity."" 
  It 
  

   states 
  that 
  the 
  velocity 
  of 
  light 
  in 
  free 
  space 
  appears 
  the 
  same 
  

   to 
  all 
  observers, 
  regardless 
  of 
  the 
  motion 
  of 
  the 
  source 
  of 
  

   light 
  or 
  of 
  the 
  observer. 
  

  

  These 
  two 
  laws 
  taken 
  together 
  constitute 
  tlie 
  principle 
  of 
  

   relativity. 
  They 
  generalize 
  a 
  number 
  of 
  experimental 
  facts, 
  

   and 
  are 
  inconsistent 
  with 
  none. 
  In 
  so 
  far 
  as 
  these 
  generali- 
  

   zations 
  go 
  beyond 
  existing 
  facts 
  they 
  require 
  further 
  verifi- 
  

   cation. 
  To 
  such 
  verification, 
  however, 
  we 
  may 
  look 
  forward 
  

   with 
  reasonable 
  confidence, 
  for 
  Einstein 
  has 
  deduced 
  from 
  

   the 
  principle 
  of 
  relativity_, 
  together 
  with 
  the 
  electromagnetic 
  

   theory, 
  a 
  number 
  of 
  striking 
  consequences 
  which 
  are 
  

   remarkably 
  self-consistent. 
  Moreover 
  the 
  system 
  of 
  mechanics 
  

   which 
  he 
  obtains 
  is 
  identical 
  with 
  the 
  non 
  - 
  Newtonian 
  

   mechanics 
  developed 
  from 
  entirely 
  different 
  premises 
  by 
  one 
  

   of 
  the 
  present 
  authors 
  J. 
  Finally, 
  one 
  of 
  the 
  most 
  important 
  

   equations 
  of 
  this 
  non-Newtonian 
  mechanics 
  has 
  within 
  the 
  

   past 
  year 
  been 
  quantitatively 
  verified 
  by 
  the 
  experiments 
  of 
  

  

  * 
  Ahhandlungen 
  iiher 
  theoretische 
  Physik, 
  Leipzig, 
  1907, 
  p. 
  443. 
  

  

  t 
  An 
  excellent 
  summary 
  of 
  the 
  conclusions 
  drawn 
  from 
  the 
  principle 
  

   of 
  relativity, 
  "by 
  Einstein, 
  Planck, 
  and 
  others 
  is 
  given 
  by 
  Einstein 
  in 
  the 
  

   Jahrhuch 
  der 
  Jkadioaktivitdt, 
  iv. 
  p. 
  411 
  (1907). 
  An 
  interesting 
  treatment 
  

   of 
  certain 
  phases 
  of 
  this 
  problem 
  is 
  given 
  by 
  Bumstead, 
  Amer. 
  Jour. 
  Sci. 
  

   xxvi. 
  p. 
  493(1908). 
  

  

  X 
  Lewis, 
  Phil. 
  Mag. 
  xvi. 
  p. 
  705 
  (1908). 
  

  

  